This invention relates to a coal liquefaction process, and more particularly, it relates to the hydrogenation of undissolved coal hydrogenation and and subsequent liquefaction thereof to provide useful hydrocarbon liquid and gas fuel products wherein solid coal particulates are hydrogenated in a coal/oil slurry of a hydrocarbon liquid solvent in the presence of a particles hydrogenation catalyst.
Conventional processes for coal liquefaction and hydrogenation include a preheating or thermal dissolution step for the coal-oil slurry feed prior to the catalyst reaction step, as generally disclosed in U.S. Pat. No. 3,519,555; 3,700,584; 3,791,957 and 4,111,788. Other coal hydrogenation processes use fine recycled catalysts at plug flow conditions and low solvent/coal ratios such as U.S. Pat. Nos. 4,090,943 and 4,102,775. In these processes, the coal-oil slurry is preheated to near the reactant temperature before feeding it into the catalytic reaction zone.
In these conventional coal hydrogenation processes which utilize the coal-slurry preheating step, the hydrogen donor potential or hydrogen concentration of the coal-derived slurrying oil therein is limited by its mobility and the hydrogen is usually consumed during the coal preheating and dissolution steps. These processes are also lacking in that the coal is not sufficiently hydrogenated to fully liquefy or convert coal to useful hydrocarbon liquids and gas fuel products as provided herein.
The conventional methods of coal liquefaction attempt to liquefy coal while having donatable hydrogen available in the solvent liquid to "seal off" free radicals which crack from the coal. Catalytic processes provide a greater quantity of hydrogen for this purpose by hydrogenating the solvent. In significant contrasts, the process of the present invention relies on substantial hydrogenation of the particulate coal in the first stage, particle but the predominant transfer of the donatable hydrogen to the coal particle takes place before the liquefaction thereof. Once the coal liquefies, the excess hydrogen in the products induces almost immediate reformation reactions which in turn result in stable, light compounds. In hydrocarbon the conventional liquefaction processes, more heavy residual products are made since the polymerization reactions, i.e., condensation, are competitive with the hydrogen transfer from solvent reformation reactions which occur much slower.
In a process developed by Qader and described in U.S. Pat. No. 4,331,530, a process for the hydrogenation of coal and subsequent treatment of hydrogenated coal to produce fuels and chemicals is provided. In this process, there is not any solvent used and the hydrogen provided in the process involves the hydrogen transfer from the gas phase to solid phase. In an attempt to hydrogenate the coal, the coal has been pulverized into very fine particles. This procedure of hydrogenating a dry coal, provides great difficulty in the hydrogenation thereof in order to liquefy or convert such coal to useful fuel products. Thus; the present coal hydrogenation and liquefaction process is needed in order to fully and more completely convert the hydrogenated coal of various types to useful low boiling hydrocarbons liquids and fuel products such as gasoline, diesel fuel oil, and naphtha.